Many compounds regarding optically active spiro quaternary ammonium salts have been known to date. Examples thereof include the compound described in Patent document 1 and represented by the following formula

and the compound described in Patent document 3, and the documents disclose that these compounds perform extremely effectively as a phase transfer catalyst for synthesizing optically active α-amino acids regardless of being natural or not. However, the optically active spiro quaternary ammonium salts described in these documents are expensive since they are constituted from two kinds of binaphthyl derivatives having different substituents, and thus they are not necessarily satisfactory for industrial use.
Moreover, the compound represented by the following formula is described in Patent document 2.
However, because the compound is optically active only on one side, the reaction time is long, and thus the compound is not necessarily satisfactory for industrial use.
Furthermore, the compound represented by the following formula is described in Patent document 4. However, since the spiro quaternary ammonium salts described in these documents are constituted of two kinds of optically active biphenyl derivatives which have the same substituents, there are limits in catalyst design, and thus the salts are not necessarily satisfactory for industrial use.

For this reason, the development of an optically active spiro quaternary ammonium salt which is effective as a phase transfer catalyst for synthesizing optically active α-amino acids and which is readily produced and is also practical, has been desired.    [Patent document 1] Japanese Laid-Open Patent Application No. 2001-48866    [Patent document 2] Japanese Laid-Open Patent Application No. 2002-326992    [Patent document 3] Japanese Laid-Open Patent Application No. 2003-81976    [Patent document 4] Japanese Laid-Open Patent Application No. 2004-359578